If I have set up cascading report parameters, the dependant parameter's value is evaluated before the data source is updated.

This can cause issues when complex expressions are used to set the value since the values of the fields won't be accurate.

For example, if I use a DateTime parameter and need to add minutes to the date based on a field from the data source, and the data is filtered based on the value of another report parameter, I have to use the IsNull() function to avoid providing a null value(because the field will be null before the data source is re-evaluated):

= AddMinutes(Today(), IsNull(First(Fields.IntervalMinute), 0))